[CP2K-user] [CP2K:22302] Question about charge settings and binding energy calculations for oleate/carboxylate adsorption on CsPbBr3 slabs in CP2K

['舒夜' via cp2k]

Dear all,

I am a beginner with CP2K. Recently, I have been trying to calculate the 
adsorption/binding energy of carboxylate ligands on a CsPbBr3 perovskite 
slab surface. Specifically, I would like to model the interaction between 
deprotonated carboxylate ligands, such as oleate (OA−) or benzoate (BA−), 
and surface Pb sites, and compare the relative binding strengths of 
different ligands.

The main issue I am facing is how to properly treat the charge of the 
deprotonated ligand in CP2K, and how to define a reliable binding energy.

So far, I have tested several models:

   1. 
   
   I removed the H atom from the carboxyl group of the acid molecule and 
   placed the deprotonated ligand near a surface Pb site of the CsPbBr3 slab, 
   while setting the total charge of the whole system to 0.
   The energy can converge in this case, but the ligand structure becomes 
   significantly distorted after geometry optimization. Therefore, I am not 
   sure whether this “H-removed but neutral total charge” model is physically 
   meaningful.
   2. 
   
   I treated the deprotonated carboxylate ligand as an anion and set the 
   total charge of the whole system to -1.
   In this case, the SCF/energy convergence shows strong oscillations, and 
   the calculated binding energy becomes abnormally large. The ligand may also 
   become distorted during optimization.
   3. 
   
   I also tried setting the slab periodicity to XY and modifying the 
   Poisson/electrostatic boundary condition settings, but I am still not sure 
   what the correct setup should be for a slab + charged adsorbate system.
   
I would like to ask the following questions:

   1. 
   
   What is the recommended way to model the adsorption of carboxylate 
   ligands such as OA−/BA− on a CsPbBr3 slab surface in CP2K?
   2. 
   
   For a deprotonated carboxylate ligand, should I directly calculate a 
   charged slab + ligand anion system? Or is it more appropriate to construct 
   an overall neutral dissociative adsorption model, for example:
   
   neutral slab + neutral acid → slab–carboxylate + H_surf
   
   where the H atom from the carboxylic acid is transferred to a surface Br 
   site, so that the whole system remains at CHARGE 0?
   3. 
   
   If a charged system such as slab + OA− is used, how should CHARGE, 
   PERIODIC, POISSON, and possible dipole/electrostatic corrections be set in 
   CP2K? Would the adsorption energy obtained from such a charged slab system 
   be reliable?
   4. 
   
   For the binding energy, which reference state is more appropriate?
   
   E_ads = E(slab + OA−) - E(slab) - E(OA−)
   
   or
   
   E_ads^diss = E(slab–OA− + H_surf) - E(slab) - E(neutral OA)
   
I would greatly appreciate any suggestions on the proper modeling strategy 
and binding energy definition.

Best regards,
Haotian Chen

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